The invention provides pigment preparations, a process for preparing pigment preparations and use thereof.
Powdered pigments are used to color thermoplastic materials. The advantage of powdered pigments is that they do not depend on the use of a support material. However, this advantage is often produced at the cost of dispersibility.
To improve dispersibility, the pigments are often coated with a resin (DE 2540355) or with polymers (U.S. Pat. No. 3,133,893).
Special drying processes are known from EP 0036520, wherein finely divided pigments and a liquid, the critical temperature of which is below the decomposition temperature of the pigment, are heated under pressure to temperatures above the critical temperature of the liquid and the pressure is then reduced to atmospheric pressure, wherein the temperature is always kept above the condensation line of the liquid.
In addition, pigment preparations are known from EP 0282855, these contain an organic pigment and/or carbon black and a surfactant selected from the group of alkylbenzene sulfonates and sulfosuccinates, and which are dried, optionally after wet-crushing, by spray-drying or freeze-drying from an aqueous medium. In the case of sulfosuccinates, the organic pigments are chosen from a specific group.
The known processes have the disadvantage that redispersibility is poor.
The object of the present invention is to prepare a pigment preparation which has good redispersibility, flow characteriztics and color intensity and a low tendency to form dust.
The invention provides a pigment preparation which contains a pigment and/or carbon black and a polymer and/or a surfactant selected from the group of cross-linked polyethylene acrylic acid, polyvinylpyrrolidone, alcohol alkoxylates, fatty alcohol polyglycol ethers, lignin sulfonates, alkylphenol polyglycol ethers, naphthalenesulfonic acid derivatives or mixtures thereof, characterized in that these are prepared by freeze-drying from aqueous dispersion.
Colored pigments may be used as pigments, for example yellow, orange, red, violet, blue, green or brown pigments. Inorganic blue pigments, for example iron blue, ultramarine blue, cobalt blue or mixed phase blue pigments, or organic blue pigments, for example phthalocyanine blue or indanthrene blue may preferably used as pigments. The carbon black used may be furnace black, gas black, channel black, lamp black or acetylene black or Si-containing carbon black, known from WO 98/45361 or DE 19613796, surface-modified carbon black, known from DE 10012783.5, DE 10012784.3, JP 11323177 or WO 96/18688, inversion black, known from DE 19521565, and metal-containing carbon blacks, known from WO 98/42778. The carbon black used may preferably be a pigment carbon black with an average particle diameter of 8 to 80 nm, preferably 10 to 35 nm, and a DBP number of 40 to 200 ml/100 g, preferably 60 to 150 ml/100 g. In a particularly preferred embodiment of the invention, gas black with an average particle diameter of 8 to 30 nm, preferably 10 to 25 nm, may be used.
The polymer may be a copolymer, block copolymer, polyampholyte or intermeshed polymer. The molecular weight Mw of the polymer may be less than 100,000 g/mol, preferably less than 10,000 g/mol. Copolymers based on (meth)acrylic acid with basic (meth)acrylates, such as dimethylaminoethyl (meth)acrylate and dimethylaminopropyl (meth)acrylamide and its quaternary ammonium compounds and also other alkyl or aryl (meth)acrylates (for example C4-30-alkyl (meth)acrylate, cyclohexyl (meth)acrylate, benzyl (meth)acrylate, phenylethyl (meth)acrylate), heterocyclic (meth)acrylates (for example morpholinoethyl (meth)acrylate, N-(2-methacryloyloxyethyl)ethylene-urea) or hydroxyesters (for example 2-hydroxyethyl (meth)acrylate, hydroxypropyl (meth)acrylate) or alkyl polyethylene glycol(200-2000)(meth)acrylates (for example methoxypolyethylene glycol-750 methacrylate) may be used. The polyampholytes used may be water-soluble polymers based on (meth)acrylic acid which have dispersing or pigment-stabilizing properties and which are also intended to prevent diffusion into the surface of paper by interacting with the carbon black pigments. The intermeshing polymers used may be graft polymers with emulsifying properties which are obtained by copolymerizing hydrophobic, terminally functionalized macromonomers with hydrophilic monomers (EP 0 728 780 B1). Macromonomers with (meth)acryloyl terminal groups are prepared, for example, from C8-C30-alkyl methacrylates, cyclohexyl methacrylate or benzyl methacrylate and are then copolymerized with hydrophilic (meth)acrylates (for example (meth)acrylic acid, (meth)acrylamide, 2-hydroxyethyl (meth)acrylate, hydroxypropyl (meth)acrylate, dimethylaminoethyl (meth)acrylate and dimethylaminopropyl (meth)acrylamide and its quaternary ammonium compounds). Block copolymers with the same monomer composition are equally suitable for use here.
Polymers which may be used are copolymers which are prepared from acrylamide monomers and at least one monomer selected from acrylic acid, dimethylamino-propylamine, dimethylaminopropylacrylamide (basic, neutral, quaternized), dimethylaminoethyl acrylate and dimethylaminoethyl methacrylate.
The polymer may be a mixture of two or more polymers.
The dispersion may contain a combination of wetting agents, such as two wetting agents.
In one embodiment of the invention, a combination of
(a) a cross-linked polyoxyethylene acrylic acid and
(b) an alkoxyethylate, preferably a fatty alcohol ethoxylate, in particular a fatty alcohol ethoxylate with 30 ethylene glycol units,
is used, wherein the ratio of surfactants a:b=1:1 to 1:10.
The pigment preparation may contain 50 to 99 wt. %, preferably 60 to 90 wt. %, of pigment and/or carbon black and 1 to 50 wt. %, preferably 10 to 40 wt. %, of surfactant and/or polymer.
All pigment dispersions which remain stable during the freezing process and do not flocculate are suitable for use in the process of freeze-drying.
The invention also provides a pigment preparation containing a self-dispersing carbon black, which is characterized in that this is prepared by freeze-drying from aqueous dispersion. Self-dispersing carbon blacks may be surface-modified carbon blacks, known from DE 10012783.5, DE 10012784.3, DE 198 24 047.3, JP 11323177 or WO 96/18688. Self-dispersing carbon blacks can form a stable dispersion in an aqueous medium without the addition of surfactants or polymers.
The invention also provides a process for preparing the pigment preparation which is characterized in that the aqueous pigment preparation is dried by freeze-drying and then optionally crushed.
To prepare the aqueous pigment preparation, pearl mills, ultrasound or an Ultra-Turrax mill may be used to form the dispersion.
Freeze-drying and drying may be performed in an ice condenser chamber. The rate of freezing can be between 0.01xc2x0 and 10xc2x0 C./min, preferably between 0.1xc2x0 and 3.0xc2x0 C./min.
The optimum freeze-drying conditions depend strongly on the product. The product temperature may be 10xc2x0 C. below the eutectic point of the samples. The reduced pressure to be set can then be deduced from the product temperature.
Carbon black dispersions according to the invention may be used for coloring purposes and/or to provide antistatic characteristics in water-based coloring and lacquer systems, disperse dyes, printing inks, inking systems and coating systems.
Pigment preparations according to the invention advantageously have a more intense color than non-freeze-dried pigment preparations.